Autonomous mobile vehicles (robots) have been designed to operate in indoor and outdoor environments. Two principal issues in vehicle guidance are: (1) general navigation within the environment; and (2) maneuvering around obstacles. With respect to the latter, a critical problem is the detection and collision avoidance of obstacles which unexpectedly lie in the path of the vehicle. The type and configuration of obstacles can occur in bewildering configurations which cannot be anticipated. In typical indoor environments, obstacles include humans, furniture, trash cans, carts, stock in store aisles, other vehicles and shelves.
Sensors used to detect such obstacles include sonar, contact sensitive bumpers, visual systems, infrared scanners, and laser ranging systems. Contact sensitive bumpers are simple and low cost but are cumbersome as a sole means of providing complete frontal coverage to detect all possible obstacles. Sonar offers longer range non-contact sensing, but many sensors are needed for full coverage, and sonar is subject to erroneous readings resulting primarily from the specular nature of sonar reflections. Multiple echoes give false "mirror" images. Smooth objects whose surfaces are not facing the sonar source reflect waves away from the receiver, rendering the obstacle invisible to sonar. Laser ranging systems offer the most complete and accurate sensing, but are too heavy, power consuming, and expensive for practical application to commercially viable mobile robots in cleaning or fetch and carry operations.
Generally, obstacles of concern may occur at any position in the frontal cross-section of the vehicle in its direction of travel. Overhanging shelves, posts, table or desk tops, hanging plants, stock on store shelves, and protruding poles may extend into the frontal cross-section. Complete coverage may be provided by putting a contact sensitive shell across the front of the entire vehicle. In that case, special holes would have to be cut as windows for the fields of view of forward looking sonar or vision.